1. Field of the Invention
This invention relates to a data processing method of a printing apparatus and the printing apparatus for printing a multicolor image on a printing medium, such as a printing paper or a film, while transporting the printing medium relative to printing heads for at least two colors. More particularly, this invention is directed to a data processing technique in a printing apparatus having printing heads being spaced away for each color in a medium-feed direction.
2. Description of the Related Art
In performing printing with use of an inkjet printing apparatus, a first method of this type conventionally includes the following. That is, the method includes transporting a printing paper, detecting a transportation speed of the printing paper, detecting a skew angle of the printing paper, correcting the transportation speed in accordance with the transportation speed and the skew angle, and controlling a discharge timing of ink droplets from two or more printing heads in accordance with the corrected transportation speed. See, for example, Japanese Patent Publication No. 2008-105347.
Moreover, printing is performed with use of an inkjet printing apparatus with a printing head that has two or more inkjet heads with ink discharging nozzles being formed in a staggered arrangement in a direction of ink droplets orthogonal with respect to a transporting direction of a printing paper while moving the printing head and a printing paper relative to each other. In this printing, a second method of this type includes, when skew occurs, discharging ink droplets in accordance with a skew angle from some of the ink discharging nozzles that are disposed adjacent to an end in the direction orthogonal with respect to the transporting direction and in the same position seen from the transporting direction, and stopping discharge of the ink droplets from some of the ink discharging nozzles. Consequently, the ink discharging nozzles in the direction orthogonal with respect to the transport direction are selectively used. See, for example, Japanese Patent Publication No. 2010-167723.
In the second method, two or more ink discharging nozzles arranged orthogonally with respect to the transport direction are switched selectively in accordance with skew of the printing paper. Consequently, variation in pitch of an edge between the inkjet heads of the printing head (a connecting portion of the inkjet heads) can be eliminated.
However, the conventional examples with such constructions have the following problems.
Specifically, the conventional first method enables to prevent deviation of ink droplets in the transport direction. On the other hand, the method cannot prevent deviations of ink droplets in the direction orthogonal with respect to the transport direction. Such problem may arise. Moreover, the conventional second method enables to prevent deviation of ink droplets within the same printing head in the direction orthogonal with respect to the transport direction. On the other hand, the method cannot prevent deviation among two or more printing heads in the direction orthogonal with respect to the transport direction. Consequently, the first and second methods cannot prevent dot deviation due to skew in the direction orthogonal with respect to the transport direction, resulting in degradation in quality of the printing image. Such problem may also arise. Moreover, ink droplets in different colors are discharged in two or more printing heads. Thus, dot deviation is very remarkable even when the deviation is slightly generated. As a result, degradation in image quality due to the dot deviation is regarded as printing failure. Accordingly, the dot deviation among the printing heads leads to a remarkable problem.